This invention relates to optoelectronic semiconductor devices, such as semiconductor laser diodes and light emitting diodes.
In various industrial fields, such as optical fiber communication systems and information systems, active efforts have been directed to the utilization of optoelectronic semiconductor devices, including semiconductor laser diodes and light emitting diodes, as key parts of such systems in order to accomplish large capacity information transmission. An optoelectronic semiconductor devices are element for converting electric signals into optical signals. Hence, attempts to arrange a signal processing circuit and optoelectronic semiconductor devices in an integrated relationship on a single substrate have recently been attracting wide attention. Such integrated circuits in which optoelectronic devices and electronic devices are integratedly arranged are called optoelectronic integrated circuits (OEIC). As a pioneer development in the field of OEIC, C. P. Lee, S. Margalit, I. Ury, and A. Yariv proposed to integrate a semiconductor laser diode and a gunn diode together on a semi-insulating GaAs (gallium arsenide) substrate, which proposal was disclosed in Applied Physics Letter 32 (12) pp 806-807 (1978). Thereafter, in Applied Physics Letter 34 (7) pp 430-431 (1979), I. Ury, S. margalit, M. Yust, and A. Yariv disclosed a semiconductor laser diode with driving circuits (LD/Driver) which comprises a semiconductor laser diode and a metal semiconductor field effect transistor (MESFET) arranged integratedly on a semi-insulating GaAs substrate.
According to the type of semiconductor substrate used, OEIC can be classified into two types; one using a GaAs substrate and the other using an indium phosphide (InP) substrate. Further-more, by the type of electronic devices integrated into the circuit, the classification is such that a MESFET is used with a GaAs substrate, while a metal insulator semiconductor field effect transistor (MISFET) is used with an InP substrate. A pioneer embodiment using a MISFET was disclosed by U. Koren, K. L. Yu, T. R. Chenn N. Bar-Chaim, S. Margalit, and A. Yariv in Applied Physics Letter 40 (8) pp 643-645 (1982). The present inventors developed an LD/Driver comprising an InP substrate and a hetero-junction bipolar transistor (HBT) as an electronic device, which was disclosed in Applied Physics Letter 45 (3) pp 191-193 (1984). As far as the integration of an HBT on an InP substrate is concerned, the LD/Driver developed by the present inventors was a pioneer one.
In the course of their research into OEICs utilizing an HBT, the inventors found that the HBT emits light in a base layer if a bias voltage is suitably selected. That is, as the supply voltage for a switch circuit using an HBT is varied, the base layer of the transistor emits light, with a varying intensity of light emission. The OEIC using an indium phosphide/indium gallium arsenide phosphide substrate as disclosed by the present inventors in Applied Physics Letter 45 (8) pp 191-193 (1984) have such an HBT integrated therein. The intensity of aforesaid light emission from the base layer depends upon the operational region of the HBT. If the supply voltage is high, the operational region of the HBT is in an active region in which the recombination of minority carriers in the base layer is unlikely to take place, so that the intensity of light emission is lower. Conversely, if the supply voltage is low, the operational region of the HBT is in a saturation region in which excess minority carriers are injected from both an emitter and a collector into the base layer and thus recombination of electrons with holes takes place in the base layer, so that the intensity of light emission becomes higher.
This invention is based on the principle of such light emission in the base layer of the aforesaid HBT. That is, the invention is such that a light-reflective resonator (e.g., Faby-Perot resonator) is formed in a base layer of an HBT, whereby lasing, i.e., the emission of a laser beam, is made possible. The control of the lasing is effected by controlling a base current.
Prior to the present invention, disclosed devices having such multiple functions as described above were described in Japanese Patent Publication No. 42-5572 (published Mar. 7, 1967), U.S. Pat. No. 3,369,132 (issued Feb. 3, 1968), and U.S. Pat. No. 3,278,814 (issued Oct. 11, 1966). In Japanese Patent Publication No. 42-5572, there is teaching as to light emission between a base layer and a collector layer in an npn type or pnp type bipolar transistor using a GaAs semiconductor material. This prior art device has disadvantages in that the arrangement of the device requires diffusion of n-type and p-type impurities into the GaAs substrate, a technique rather impracticable in the state of the art. U.S. Pat. Nos. 3,369,132 and 3,278,814 disclose a pnp-type or npn-type bipolar structure, as is the case with Japanese Patent Publication No. 42-5572, but these disclosures relate merely to a device arranged such that light emitted between a base and an emitter is absorbed between the base and a collector for supply as an external output current.